Airflow control devices based on active materials

ABSTRACT

An airflow control device comprises a body and an active material in operative communication with the body. The active material, such as shape memory material, is operative to change at least one attribute in response to an activation signal. The active material can change its shape, dimensions and/or stiffness producing a change in at least one feature of the airflow control device such as shape, dimension, location, orientation, and/or stiffness to control vehicle airflow to better suit changes in driving conditions such as weather, ground clearance and speed, while reducing maintenance and the level of failure modes. As such, the device reduces vehicle damage due to inadequate ground clearance, while increasing vehicle stability and fuel economy. An activation device, controller and sensors may be employed to further control the change in at least one feature of the airflow control device such as shape, dimension, location, orientation, and/or stiffness of the device. A method for controlling vehicle airflow selectively introduces an activation signal to initiate a change of at least one feature of the device that can be reversed upon discontinuation of the activation signal.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of, and claims priority to, U.S.patent application Ser. No. 11/086,469, filed on Nov. 5, 2004,incorporated herein in its entirety.

BACKGROUND

The present disclosure relates to devices for controlling vehicleairflow and, more particularly, to devices for controlling vehicleairflow which can be adjusted through changes in active materials inresponse to varying conditions, the adjustment being affected throughshape, dimension, and/or stiffness changes in the active material.

Airflow over, under, around, and/or through a vehicle can affect manyaspects of vehicle performance including vehicle drag, vehicle lift anddown force, and cooling/heat exchange for a vehicle powertrain and airconditioning systems. Reductions in vehicle drag improve fuel economy.Vehicle lift and downforce can affect vehicle stability and handling. Asused herein, the term “airflow” refers to the motion of air around andthrough parts of a vehicle relative to either the exterior surface ofthe vehicle or surfaces of elements of the vehicle along which exteriorairflow can be directed such as surfaces in the engine compartment. Theterm “drag” refers to the resistance caused by friction in a directionopposite that of the motion of the center of gravity for a moving bodyin a fluid. The term “lift” as used herein refers to the component ofthe total force due to airflow relative to a vehicle acting on thevehicle in a vertically upward direction. The term “downforce” usedherein refers to the component of total force due to airflow relative tothe vehicle acting on a vehicle in a vertically downward direction.

Devices known in the art of vehicle manufacture to control airflowrelative to a vehicle are generally of a predetermined, non-adjustablegeometry, location, orientation and stiffness. Such devices generally donot adapt as driving conditions change, thus the airflow relative to thevehicle cannot be adjusted to better suit the changing drivingconditions. Additionally, current under-vehicle airflow control devicescan reduce ground clearance. Vehicle designers are faced with thechallenge of controlling the airflow while maintaining sufficient groundclearance to avoid contact with and damage by parking ramps, parkingblocks, potholes, curbs and the like. Further, inclement weather, suchas deep snow slush or rainfall, can damage the device and/or impairvehicle handing.

Current stationary airflow control devices may be adjustable by mountingand/or connecting the devices to hydraulic, mechanical, electricalactuators and/or the like. For example, some vehicle spoilers may adjustlocation and/or orientation in response to an actuator signal. However,such actuators generally require additional components such as pistons,motors, solenoids and/or like mechanisms for activation, which increasethe complexity of the device often resulting in increased failure modes,maintenance, and manufacturing costs. Therefore, there exists a need foran adjustable device for controlling vehicle airflow under varyingdriving conditions that enhances device simplicity while reducing deviceproblems and the number of failure modes.

BRIEF SUMMARY

Disclosed herein is an airflow control device for a vehicle, i.e. airdeflector. The air deflector comprises a body portion having at leastone surface, and an active material in operative communication with theat least one surface, the active material being operative to change atleast one attribute in response to an activation signal, wherein anairflow across the air deflector changes with the change in the at leastone attribute of the active material.

Also disclosed is a system for controlling vehicle airflow comprising astationary surface of a vehicle; and an air deflector fixedly attachedto the stationary surface, the air deflector comprising an airdeflecting body having at least one surface, an active material inoperative communication with the at least one surface, the activematerial being operative to change a feature of the deflecting body inresponse to an activation signal, and an activation device in functionalcommunication with the active material, the activation device beingoperable to selectively provide the activation signal, the activationsignal initiates a change in at least one attribute of the activematerial, wherein the change in at least one attribute of the activematerial changes a feature of the air deflecting body.

A method for controlling vehicle airflow is also disclosed positioningan airflow controlling device on a stationary surface of the vehicle,the airflow controlling device comprising a body having at least onesurface, and an active material in operative communication with the atleast one surface, the active material being operative to change a atleast one attribute in response to an activation signal; selectivelyintroducing the activation signal upon meeting and/or exceeding apredetermined vehicle condition; and changing the at least one attributeof the active material from a first at least one attribute to a secondat least one attribute.

In another embodiment, an air deflector for a vehicle comprises anactive material comprising an elongated body having one end fixedlyattached to a stationary surface, wherein the active material is adaptedto change a flexural modulus property in response to an activationsignal.

In yet another embodiment, an air deflector for a vehicle comprises ahinge comprising an active material adapted to hingingly communicatewith a stationary surface, wherein the active material is adapted tochange a flexural modulus property in response to an activation signal;and a rigid flap fixedly attached to the hinge.

A method of operating an air deflector comprises activating an activematerial to change at least one attribute of the active material,wherein the air deflector comprises an elongated body of the activematerial having one end fixedly attached to a stationary surface and another end in an impinging airflow path, wherein the change in the atleast one attribute changes a deflection angle of the air deflector.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are meant to be exemplaryembodiments, and wherein the like elements are numbered alike:

FIG. 1 is a perspective view of an airflow control device in accordancewith the present disclosure;

FIGS. 2 a and 2 b are perspective views of an airflow control devicehaving an active material on a surface in accordance with the presentdisclosure;

FIG. 3 a is a perspective view of an airflow control device havingactive material embedded within a surface of the body in accordance withan embodiment of the present disclosure;

FIG. 3 b is a perspective view of an airflow device having activematerial embedded within the body in accordance with an embodiment ofthe present disclosure;

FIG. 4 is a perspective view of an airflow control device wherein anactive material is connected externally to the surface of the airflowcontrol device in accordance with an embodiment of the presentdisclosure;

FIG. 5 is a perspective view of an airflow control device in accordancewith an embodiment of the present disclosure;

FIG. 6 is a side view of the airflow control device of FIG. 5;

FIG. 7 is a front plan view of an airflow control device in accordancewith an embodiment of the present disclosure;

FIG. 8 is a side view of the airflow control device of FIG. 7; and

FIG. 9 is a perspective view of an airflow control device and latchmechanism in accordance with another embodiment.

DETAILED DESCRIPTION

The present disclosure provides an airflow control device for a vehicle100 (FIG. 7), wherein the airflow control device is capable ofreversibly changing shape, dimension, orientation, location and/orstiffness, the change being effected through the activation of an activematerial, allowing the airflow control device to adapt to varyingdriving conditions. Employing the active materials as described hereinadvantageously provides an actuation mechanism that is lightweight,inherently robust, and lower in complexity than prior external actuationmeans. Moreover, the airflow control devices described herein are alsoof low cost and of easily adaptable design that may be integrated withlimited changes to the existing structure. As used herein the term“vehicles” includes any structure subject to airflow including, but notintended to be limited to, automobiles, over the highway tractors,boats, motorcycles, airplanes, bobsleds, spaceship, and the like.

As shown in FIG. 1, an airflow control device for a vehicle (alsoreferred to herein as an air deflector), generally indicated asreference numeral 10, comprises a body portion 12 having at least onesurface 13, 14, 15 and an active material 16 in operative communicationwith at least one surface 13, 14, 15 and/or the body 12, the activematerial 16 having a first at least one attribute that is operative tochange in response to an activation signal 17 (FIG. 8) to the activematerial 16. An attribute of the active material 16, and changesthereof, refer to characteristics of the active material 16 such as, butnot limited to, shape, dimension, stiffness, combinations thereof, andthe like. The changes in at least one attribute of the active material16 affect various features of the airflow device 10 such as, but notlimited to, shape, dimension, location, orientation, stiffness,combinations thereof, and/or the like, resulting in a change in theairflow across the device 10. In this manner, the device 10 isadjustable and airflow across the device 10 changes with the change inat least one attribute of the active material 16 under varying drivingconditions.

Using an automobile as an example, the airflow control device 10 may beof any of a variety of configurations, including but not limited to, airdams; fender flares; side skirt cribs; cabs; rear and tailgate spoilers;louvers for controlling airflow through radiator, other heat exchangers,the engine compartment, over the drive train and transmission; and airand wind deflectors for roof tops, sunroofs, vent windows; and likeconfigurations. An exemplary air dam comprises a projection of the bodyshell underneath the front of the chassis of a vehicle and functions toreduce the amount of air turbulence and drag underneath the vehicle, aswell as channels cooling air to the radiator. Further, many airflowcontrol devices, and air deflectors in particular, improve vehiclestability and increase gas mileage. For example, at low speeds the airdam can be actively positioned so that additional ground clearance isprovided, such as may be desired to clear speed bumps, provide curbclearance for parking, and the like. At higher speeds, the air dam canbe actively positioned to divert the incoming airflow into the coolingsystem, or divert air about the vehicle to improve aerodynamics, improvevehicle stability, increase gas mileage, and the like. It will beunderstood that the device 10 may be a portion of a vehicle louversystem and/or an independent component of the vehicle.

The body 12 (also referred to herein as an air deflecting body) may beany of a variety of materials and configurations that enable the airflowdevice 10 to function, and may further comprise at least one surface 13,14, or 15. In one embodiment, the body 12 is comprised of a flexiblematerial that exhibits adequate flexibility to operate as an adjustableairflow control device as the active material 16 changes at least oneattribute. In an additional embodiment, the body 12 may comprise one ormore active material 16. The active material 16 may change at least oneattribute in response to an activation signal, and revert back to theoriginal state of the at least one attribute upon discontinuation of theactivation signal, or, for the classes of active materials that do notautomatically revert upon discontinuation of the activation signal,alternative means can be employed to revert the active materials totheir original state as will be discussed in detail herein. In thismanner, the airflow control device 10 functions to adjust to changingdriving conditions while increasing device simplicity and reducing thenumber of failure modes.

Active material 16 includes those compositions that can exhibit a changein stiffness properties, shape and/or dimensions in response to theactivation signal, which can take the type for different activematerials 16, of electrical, magnetic, thermal and like fields.Preferred active materials 16 include but are not limited to the classof shape memory materials, and combinations thereof. Shape memorymaterials generally refer to materials or compositions that have theability to remember their original at least one attribute such as shape,which can subsequently be recalled by applying an external stimulus, aswill be discussed in detail herein. As such, deformation from theoriginal shape is a temporary condition. In this manner, shape memorymaterials can change to the trained shape in response to an activationsignal. Exemplary active materials include shape memory alloys (SMA),shape memory polymers (SMP), electroactive polymers (EAP), ferromagneticSMAs, electrorheological fluids (ER), magnetorheological fluids (MR),dielectric elastomers, ionic polymer metal composites (IPMC),piezoelectric polymers, piezoelectric ceramics, various combinations ofthe foregoing materials, and the like.

Shape memory alloys (SMA's) generally refer to a group of metallicmaterials that demonstrate the ability to return to some previouslydefined shape or size when subjected to an appropriate thermal stimulus.Shape memory alloys are capable of undergoing phase transitions in whichtheir yield strength, stiffness, dimension and/or shape are altered as afunction of temperature. The term “yield strength” refers to the stressat which a material exhibits a specified deviation from proportionalityof stress and strain. Generally, in the low temperature, or martensitephase, shape memory alloys can be plastically deformed and upon exposureto some higher temperature will transform to an austenite phase, orparent phase, returning to their shape prior to the deformation.Materials that exhibit this shape memory effect only upon heating arereferred to as having one-way shape memory. Those materials that alsoexhibit shape memory upon re-cooling are referred to as having two-wayshape memory behavior.

Shape memory alloys exist in several different temperature-dependentphases. The most commonly utilized of these phases are the so-calledmartensite and austenite phases discussed above. In the followingdiscussion, the martensite phase generally refers to the moredeformable, lower temperature phase whereas the austenite phasegenerally refers to the more rigid, higher temperature phase. When theshape memory alloy is in the martensite phase and is heated, it beginsto change into the austenite phase. The temperature at which thisphenomenon starts is often referred to as austenite start temperature(As). The temperature at which this phenomenon is complete is called theaustenite finish temperature (Af). When the shape memory alloy is in theaustenite phase and is cooled, it begins to change into the martensitephase, and the temperature at which this phenomenon starts is referredto as the martensite start temperature (Ms). The temperature at whichaustenite finishes transforming to martensite is called the martensitefinish temperature (Mf). Generally, the shape memory alloys are softerand more easily deformable in their martensitic phase and are harder,stiffer, and/or more rigid in the austenitic phase. In view of theforegoing, a suitable activation signal for use with shape memory alloysis a thermal activation signal having a magnitude to causetransformations between the martensite and austenite phases.

Shape memory alloys can exhibit a one-way shape memory effect, anintrinsic two-way effect, or an extrinsic two-way shape memory effectdepending on the alloy composition and processing history. Annealedshape memory alloys typically only exhibit the one-way shape memoryeffect. Sufficient heating subsequent to low-temperature deformation ofthe shape memory material will induce the martensite to austenite typetransition, and the material will recover the original, annealed shape.Hence, one-way shape memory effects are only observed upon heating.Active materials comprising shape memory alloy compositions that exhibitone-way memory effects do not automatically reform, and will likelyrequire an external mechanical force to reform the shape that waspreviously suitable for airflow control.

Intrinsic and extrinsic two-way shape memory materials are characterizedby a shape transition both upon heating from the martensite phase to theaustenite phase, as well as an additional shape transition upon coolingfrom the austenite phase back to the martensite phase. Active materials16 that exhibit an intrinsic shape memory effect are fabricated from ashape memory alloy composition that will cause the active materials 16to automatically reform themselves as a result of the above noted phasetransformations. Intrinsic two-way shape memory behavior must be inducedin the shape memory material through processing. Such procedures includeextreme deformation of the material while in the martensite phase,heating-cooling under constraint or load, or surface modification suchas laser annealing, polishing, or shot-peening. Once the material hasbeen trained to exhibit the two-way shape memory effect, the shapechange between the low and high temperature states is generallyreversible and persists through a high number of thermal cycles. Incontrast, active materials 16 that exhibit the extrinsic two-way shapememory effects are composite or multi-component materials that combine ashape memory alloy composition that exhibits a one-way effect withanother element that provides a restoring force to reform the originalshape.

The temperature at which the shape memory alloy remembers its hightemperature form when heated can be adjusted by slight changes in thecomposition of the alloy and through heat treatment. In nickel-titaniumshape memory alloys, for instance, it can be changed from above about100° C. to below about −100° C. The shape recovery process occurs over arange of just a few degrees and the start or finish of thetransformation can be controlled to within a degree or two depending onthe desired application and alloy composition. The mechanical propertiesof the shape memory alloy vary greatly over the temperature rangespanning their transformation, typically providing the airflow controldevices with shape memory effects, superelastic effects, and highdamping capacity.

Suitable shape memory alloy materials include, without limitation,nickel-titanium based alloys, indium-titanium based alloys,nickel-aluminum based alloys, nickel-gallium based alloys, copper basedalloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold,and copper-tin alloys), gold-cadmium based alloys, silver-cadmium basedalloys, indium-cadmium based alloys, manganese-copper based alloys,iron-platinum based alloys, iron-platinum based alloys, iron-palladiumbased alloys, and the like. The alloys can be binary, ternary, or anyhigher order so long as the alloy composition exhibits a shape memoryeffect, e.g., change in shape orientation, damping capacity, and thelike. For example, a nickel-titanium based alloy is commerciallyavailable under the trademark NITINOL from Shape Memory Applications,Inc.

Shape memory polymers (SMP's) are known in the art and generally referto a group of polymeric materials that demonstrate the ability to returnto some previously defined shape when subjected to an appropriatethermal stimulus. Shape memory polymers are capable of undergoing phasetransitions in which their shape is altered as a function oftemperature. Generally, SMP's have two main segments, a hard segment anda soft segment. The previously defined or permanent shape can be set bymelting or processing the polymer at a temperature higher than thehighest thermal transition followed by cooling below that thermaltransition temperature. The highest thermal transition is usually theglass transition temperature (Tg) or melting point of the hard segment.A temporary shape can be set by heating the material to a temperaturehigher than the Tg or the transition temperature of the soft segment,but lower than the Tg or melting point of the hard segment. Thetemporary shape is set while processing the material at the transitiontemperature of the soft segment followed by cooling to fix the shape.The material can be reverted back to the permanent shape by heating thematerial above the transition temperature of the soft segment.

In a preferred embodiment, the permanent shape of the active material 16is a substantially straightened shape and the temporary shape of theactive material 16 is a curved shape (see FIGS. 2 a-2 b). In anotherembodiment, the shape memory polymer comprises two permanent shapes. Inthe first permanent shape the active materials 16 are in a substantiallystraightened shape and in the second permanent shape, the activematerials 16 are in a curved shape.

The temperature needed for permanent shape recovery can be set at anytemperature between about −63° C. and about 120° C. or above.Engineering the composition and structure of the polymer itself canallow for the choice of a particular temperature for a desiredapplication. A preferred temperature for shape recovery is greater thanor equal to about −30° C., more preferably greater than or equal toabout 0° C., and most preferably a temperature greater than or equal toabout 50° C. Also, a preferred temperature for shape recovery is lessthan or equal to about 120° C., and most preferably less than or equalto about 120° C. and greater than or equal to about 80° C.

Suitable shape memory polymers include thermoplastics, thermosets,interpenetrating networks, semi-interpenetrating networks, or mixednetworks. The polymers can be a single polymer or a blend of polymers.The polymers can be linear or branched thermoplastic elastomers withside chains or dendritic structural elements. Suitable polymercomponents to form a shape memory polymer include, but are not limitedto, polyphosphazenes, poly(vinyl alcohols), polyamides, polyesteramides, poly(amino acid)s, polyanhydrides, polycarbonates,polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols,polyalkylene oxides, polyalkylene terephthalates, polyortho esters,polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters,polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers,polyether amides, polyether esters, and copolymers thereof. Examples ofsuitable polyacrylates include poly(methyl methacrylate), poly(ethylmethacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate),poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecylacrylate). Examples of other suitable polymers include polystyrene,polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinatedpolybutylene, poly(octadecyl vinyl ether) ethylene vinyl acetate,polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate),polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (blockcopolymer), poly(caprolactone) dimethacrylate-n-butyl acrylate,poly(norbornyl-polyhedral oligomeric silsequioxane), polyvinylchloride,urethane/butadiene copolymers, polyurethane block copolymers,styrene-butadiene-styrene block copolymers, and the like.

The active material 16 may also comprise an electroactive polymer suchas ionic polymer metal composites, conductive polymers, piezoelectricmaterial and the like. As used herein, the term “piezoelectric” is usedto describe a material that mechanically deforms when a voltagepotential is applied, or conversely, generates an electrical charge whenmechanically deformed.

Suitable MR elastomer materials include, but are not intended to belimited to, an elastic polymer matrix comprising a suspension offerromagnetic or paramagnetic particles, wherein the particles aredescribed above. Suitable polymer matrices include, but are not limitedto, poly-alpha-olefins, natural rubber, silicone, polybutadiene,polyethylene, polyisoprene, and the like.

Electroactive polymers include those polymeric materials that exhibitpiezoelectric, pyroelectric, or electrostrictive properties in responseto electrical or mechanical fields. The materials generally employ theuse of compliant electrodes that enable polymer films to expand orcontract in the in-plane directions in response to applied electricfields or mechanical stresses. An example of an electrostrictive-graftedelastomer with a piezoelectric poly(vinylidenefluoride-trifluoro-ethylene) copolymer. This combination has the abilityto produce a varied amount of ferroelectric-electrostrictive molecularcomposite systems. These may be operated as a piezoelectric sensor oreven an electrostrictive actuator.

Materials suitable for use as an electroactive polymer may include anysubstantially insulating polymer or rubber (or combination thereof) thatdeforms in response to an electrostatic force or whose deformationresults in a change in electric field. Exemplary materials suitable foruse as a pre-strained polymer include silicone elastomers, acrylicelastomers, polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example.

Materials used as an electroactive polymer may be selected based on oneor more material properties such as a high electrical breakdownstrength, a low modulus of elasticity (for large or small deformations),a high dielectric constant, and the like. In one embodiment, the polymeris selected such that is has an elastic modulus at most about 100 MPa.In another embodiment, the polymer is selected such that is has amaximum actuation pressure between about 0.05 MPa and about 10 MPa, andpreferably between about 0.3 MPa and about 3 MPa. In another embodiment,the polymer is selected such that is has a dielectric constant betweenabout 2 and about 20, and preferably between about 2.5 and about 12. Thepresent disclosure is not intended to be limited to these ranges.Ideally, materials with a higher dielectric constant than the rangesgiven above would be desirable if the materials had both a highdielectric constant and a high dielectric strength. In many cases,electroactive polymers may be fabricated and implemented as thin films.Thicknesses suitable for these thin films may be below 50 micrometers.

As electroactive polymers may deflect at high strains, electrodesattached to the polymers should also deflect without compromisingmechanical or electrical performance. Generally, electrodes suitable foruse may be of any shape and material provided that they are able tosupply a suitable voltage to, or receive a suitable voltage from, anelectroactive polymer. The voltage may be either constant or varyingover time. In one embodiment, the electrodes adhere to a surface of thepolymer. Electrodes adhering to the polymer are preferably compliant andconform to the changing shape of the polymer. Correspondingly, thepresent disclosure may include compliant electrodes that conform to theshape of an electroactive polymer to which they are attached. Theelectrodes may be only applied to a portion of an electroactive polymerand define an active area according to their geometry. Various types ofelectrodes suitable for use with the present disclosure includestructured electrodes comprising metal traces and charge distributionlayers, textured electrodes comprising varying out of plane dimensions,conductive greases such as carbon greases or silver greases, colloidalsuspensions, high aspect ratio conductive materials such as carbonfibrils and carbon nanotubes, and mixtures of ionically conductivematerials.

Materials used for electrodes of the present disclosure may vary.Suitable materials used in an electrode may include graphite, carbonblack, colloidal suspensions, thin metals including silver and gold,silver filled and carbon filled gels and polymers, and ionically orelectronically conductive polymers. It is understood that certainelectrode materials may work well with particular polymers and may notwork as well for others. By way of example, carbon fibrils work wellwith acrylic elastomer polymers while not as well with siliconepolymers.

The active material may also comprise a piezoelectric material. Also, incertain embodiments, the piezoelectric material may be configured as anactuator for providing rapid deployment. As used herein, the term“piezoelectric” is used to describe a material that mechanically deforms(changes shape) when a voltage potential is applied, or conversely,generates an electrical charge when mechanically deformed. Preferably, apiezoelectric material is disposed on strips of a flexible metal orceramic sheet. The strips can be unimorph or bimorph. Preferably, thestrips are bimorph, because bimorphs generally exhibit more displacementthan unimorphs.

One type of unimorph is a structure composed of a single piezoelectricelement externally bonded to a flexible metal foil or strip, which isstimulated by the piezoelectric element when activated with a changingvoltage and results in an axial buckling or deflection as it opposes themovement of the piezoelectric element. The actuator movement for aunimorph can be by contraction or expansion. Unimorphs can exhibit astrain of as high as about 10%, but generally can only sustain low loadsrelative to the overall dimensions of the unimorph structure. Acommercial example of a pre-stressed unimorph is referred to as“THUNDER”, which is an acronym for THin layer composite UNimorphferroelectric Driver and sEnsoR. THUNDER is a composite structureconstructed with a piezoelectric ceramic layer (for example, leadzirconate titanate), which is electroplated on its two major faces. Ametal pre-stress layer is adhered to the electroplated surface on atleast one side of the ceramic layer by an adhesive layer (for example,“LaRC-SI®” developed by the National Aeronautics and SpaceAdministration (NASA)). During manufacture of a THUNDER actuator, theceramic layer, the adhesive layer, and the first pre-stress layer aresimultaneously heated to a temperature above the melting point of theadhesive, and then subsequently allowed to cool, thereby re-solidifyingand setting the adhesive layer. During the cooling process the ceramiclayer becomes strained, due to the higher coefficients of thermalcontraction of the metal pre-stress layer and the adhesive layer than ofthe ceramic layer. Also, due to the greater thermal contraction of thelaminate materials than the ceramic layer, the ceramic layer deformsinto an arcuate shape having a generally concave face.

In contrast to the unimorph piezoelectric device, a bimorph deviceincludes an intermediate flexible metal foil sandwiched between twopiezoelectric elements. Bimorphs exhibit more displacement thanunimorphs because under the applied voltage one ceramic element willcontract while the other expands. Bimorphs can exhibit strains up toabout 20%, but similar to unimorphs, generally cannot sustain high loadsrelative to the overall dimensions of the unimorph structure.

Suit-able piezoelectric materials include inorganic compounds, organiccompounds, and metals. With regard to organic materials, all of thepolymeric materials with non-centrosymmetric structure and large dipolemoment group(s) on the main chain or on the side-chain, or on bothchains within the molecules, can be used as candidates for thepiezoelectric film. Examples of suitable polymers include, for example,but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), polyS-119 (poly(vinylamine)backbone azo chromophore), and their derivatives;polyfluorocarbons, including polyvinylidene fluoride (“PVDF”), itsco-polymer vinylidene fluoride (“VDF”), trifluoroethylene (TrFE), andtheir derivatives; polychlorocarbons, including poly(vinyl chloride)(“PVC”), polyvinylidene chloride (“PVC2”), and their derivatives;polyacrylonitriles (“PAN”), and their derivatives; polycarboxylic acids,including poly(methacrylic acid (“PMA”), and their derivatives;polyureas, and their derivatives; polyurethanes (“PUE”), and theirderivatives; bio-polymer molecules such as poly-L-lactic acids and theirderivatives, and membrane proteins, as well as phosphate bio-molecules;polyanilines and their derivatives, and all of the derivatives oftetramines; polyimides, including Kapton molecules and polyetherimide(“PEI”), and their derivatives; all of the membrane polymers;poly(N-vinyl pyrrolidone) (“PVP”) homopolymer, and its derivatives, andrandom PVP-co-vinyl acetate (“PVAc”) copolymers; and all of the aromaticpolymers with dipole moment groups in the main-chain or side-chains, orin both the main-chain and the side-chains, and mixtures thereof.

Further, piezoelectric materials can include Pt, Pd, Ni, Ti, Cr, Fe, Ag,Au, Cu, and metal alloys and mixtures thereof. These piezoelectricmaterials can also include, for example, metal oxide such as SiO₂,Al₂O₃, ZrO₂, TiO₂, SrTiO₃, PbTiO₃, BaTiO₃, FeO₃, Fe₃O₄, ZnO, andmixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS,GaAs, AgCaSe₂, ZnSe, GaP, InP, ZnS, and mixtures thereof.

Suitable active materials also comprise magnetorheological (MR)compositions, such as MR elastomers, which are known as “smart”materials whose rheological properties can rapidly change uponapplication of a magnetic field. MR elastomers are suspensions ofmicrometer-sized, magnetically polarizable particles in a thermosetelastic polymer or rubber. The stiffness of the elastomer structure isaccomplished by changing the shear and compression/tension moduli byvarying the strength of the applied magnetic field. The MR elastomerstypically develop structure when exposed to a magnetic field in aslittle as a few milliseconds. Discontinuing the exposure of the MRelastomers to the magnetic field reverses the process and the elastomerreturns to its lower modulus state.

The airflow control device 10, illustrated in FIG. 1, may comprise oneor more of the above noted active materials 16 applied as a coating, alayer, and/or sections such as strips to at least one surface 13, 14,and/or 15 of the body 12. In one embodiment, different active materialsare applied to a surface 13, 14, 15, wherein the different activematerials 16 are applied adjacent to one another. In another embodiment,the active material 16 may comprise a composite of different shapememory materials. In either embodiment, the active material 16 providesthe airflow device 10 with a shape changing capability that can beactively-tuned to a particular application, as will be described ingreater detail.

Coupled to and in operative communication with airflow device 10 is anactivation device 18. The activation device 18 is in functionalcommunication with the airflow device 10 and/or active material 16,which is operable to selectively provide an activation signal to theairflow control device 10 and change a feature of the airflow device 10by changing at least one attribute of the active material 16. Forexample, in the case of an underflow airflow device, the active material16 can retract or extend the airflow device 10 depending on the speed ofthe vehicle. The activation device 18, on demand, provides theactivation signal or stimulus to the active material 16 of the airflowdevice 10 to cause the change in one or more feature of at least aportion of the device 10. In one embodiment, the change in featuregenerally remains for the duration of the applied activation signal.Upon discontinuation of the activation signal, the active material 16generally reverts to an unpowered form and returns substantially to theoriginal at least one attribute, thus reverting the airflow device 10 tothe original feature and/or features. In another embodiment, the changein one or more attribute of the active material 16 and/or feature of atleast a portion of the device 10 may remain upon discontinuing theactivation signal. In this embodiment, the device 10 includes a means tomaintain the change in active material 16, such as a latch, lock, stopand/or the like. Upon release of the means, the device 10 reverts backto the original at least one feature. The illustrated device 10 isexemplary only and is not intended to be limited to any particularshape, size, dimension or configuration, material, or the like.

In another embodiment, the airflow device 10 includes at least onesensor 26 in operative communication with the airflow control device 10and/or the active material 16, wherein the sensor is adapted to transmitsignals indicative of at least one vehicle condition. This embodimentmay further comprise a controller 24 that is operatively connected tothe sensor 26 and activation device 18, wherein the controller isprogrammed and configured to cause the activation device 18 to providean activation signal to the active material 16 when the sensor 26signals indicate a predetermined vehicle condition.

The present disclosure is not intended to be limited to any particularactivation signal. The particular activation signal will depend on thesensitivity of the active material 16. As such, the activation signalmay provide a thermal activation signal, magnetic activation signal,electrical activation signal, chemical activation signal, and/or otherlike activation signal or combination of activation signals.

As shown in FIGS. 2 a and 2 b, perspective views of an airflow controldevice designated as reference numeral 20, an airflow device 20 maycomprise one or more surfaces 13, 14, 15 to control airflow. In oneembodiment, the body 12 of the airflow device 20 may be comprised of asuitable active material 16. In another embodiment, the body 12 maycomprise active material 16 or other suitable compositions, having oneor more surfaces 13, 14, 15 comprising one or more active materials 16.The active materials 16 in this device 20 as shown in FIG. 2 a, may havea substantially straight shape at room temperature and, as show in FIG.2 b, a curved shape (i.e. curvilinear shape) when heated above atemperature range that may be generally encountered during vehicleoperation. In this view, the airflow device 20 may control airflow whilemaintaining sufficient ground clearance to avoid contact with and damageby road hazards and inclement weather residue. In this embodiment, theactive material is preferably selected to be sensitive to thermalactivation.

As shown, one of more wires 22 are embedded in the active material 16 ofthe device 20 to provide a thermal activation means in the form ofresistive heating. In additional embodiments, controls such ascontroller 24 and/or sensor 26 may cause a current to flow through theembedded wires 22 at low driving speed causing the active material 16 tocurve upward, assuming a trained higher temperature shape. This mayresult in a rise in the airflow control device 20 and in doing soincrease vehicle ground clearance. Further, when driving above apredetermined speed, the controller 24 may discontinue the current andallow the airflow control device 20 to cool, thus straighten and deploy.In another embodiment, the change in feature may be reversed such thatat higher vehicle speeds heating may be employed to achieve a hightemperature shape, and current would be discontinued at lower vehiclespeed to achieve a low temperature shape. In another embodiment, thechange in one or more attribute of the active material 16 and/or featureof the device 10 may remain upon discontinuing the activation signal. Inthis embodiment, the device 10 includes a means to maintain the changein active material 16, such as a latch, lock, stop and/or the like. Uponrelease of the means to maintain the change in active material 16, thedevice 10 reverts back to the original at least one feature. In thismanner, the device 20 may curve upward in response to the activationsignal, maintain the upward curve until release of the means, where uponthe device 20 will revert and straighten. Further, the airflow controldevice 20 that becomes deformed, such as during an impact, may berestored or healed to a desired shape by applying the appropriatetemperature range. The selection of material comprising the body 12and/or active material 16 will be determined by the desired application.Moreover, selection of the locking means is well within the skill ofthose in the art.

As shown in FIGS. 3 a and 3 b, perspective views of an airflow controldevice designated as reference numeral 30, is shown, having stripsand/or sections of active material 16. In FIG. 3 a, the device 30comprises strips and/or sections of active material 16 embedded on oneor more surfaces 13, 14, 15, of the body 12. In an alternate view, shownin FIG. 3 b, the strips and/or sections of active material 16 areembedded within the body 12 of the device 30. In this embodiment, thebody 12 comprises a flexible matrix material with strips of activematerial 16, preferably but not necessarily, embedded at regularintervals. The placement of the active material 16 is not limited to anyparticular configuration or pattern and will be determined by thedesired application of the device 30. In one embodiment, as in strips ofSMA, the active material 16 has a trained curved shape in the austenitephase, not shown in this view. At standing or low vehicle speeds, theactive material 16 may be activated such as by resistance heating whichmay cause the active material 16 to curve and in doing so curl theairflow control device 30 up and out of the external airflow. The changein shape may be initiated by an activation signal transmitted byactivation device 18, controller 24, and/or sensor 26.

With regard to SMAs, as a result of the change in phase, the stiffnessin the austenite phase will be greater than the stiffness in themartensite phase. The number and size of the embedded active materialstrips may be chosen such that when in the austenite phase the embeddedactive material 16 causes the bulk of the airflow control device 30 todeform. However, when the active material 16 is in the martensite phase,the flexible material comprising the bulk of the airflow control device30 is sufficiently stiff to return the device 30 to a straight, deployedconfiguration, and in doing so straightening the active material 16. Athigher speeds, in excess of a predetermined vehicle speed, the currentflow causing resistant heating may be stopped, causing the activematerial 16 to return to the martensite phase. In this manner, theairflow control device 30 reverts to a straightened deployed state. Aspreviously discussed, the airflow control device 30 may be restored ifdeformed as a result of force, such as an impact, due to plasticdeformation of the strips of active material 16 by heating the activematerial 16 to the austenite phase temperature. The other activematerials noted above can be activated in a similar manner using asuitable activation signal particular to the selected active material aswill be appreciated by those skilled in the art in view of thisdisclosure.

In an additional embodiment, shown in FIG. 4, a perspective view of anairflow control device 40 comprises active material 16 in the shape ofhelical springs positioned in functional operation to the body 12 of theairflow control device 40. In this embodiment, the active material 16may be connected externally either directly or remotely to a surface 13,14, 15 of the airflow control device 40. As shown in FIG. 4, a surface13 of the body 12 is coupled with a tube 42 in such a fashion that thetube 42 is free to rotate about its axis. A spring mechanism 44 and theactive material 16 are both coupled to the tube 42 in an opposingfashion such that their respective tensions balance each other. In thismanner, the rotation of the tube 42 through external means may increasethe tension in one while reducing tension in the other. At low vehiclespeeds (i.e., less than a predetermined speed), tension in the springmechanism 44 combined with reduced stiffness and greater length of anunheated active material 16 results in rotation of the airflow controldevice 40 out of the airflow. At higher speed (i.e., greater than thepredetermined speed), the temperature of the active material 16 israised through resistance heating to produce a phase change in theactive material 16 from the martensite phase to the austenite phase. Thewires comprised of active material 16 preferably exhibit up to about a 4percent (%) reduction in length with an up to 3 times increase instiffness properties. In this manner, the combined reduction in lengthand increase in stiffness properties can result in deployment of theairflow control device 40, e.g., such as rotation of the tube 42 andstretching of the counter-balancing spring mechanism 44. Upondiscontinuation of the resistance heating, the active material 16 coolsto the martensite phase and the stretched spring mechanism 44 can beused to return the airflow control device 40 to a stowed position. Inanother embodiment, the change in one or more attribute of the activematerial 16 and/or feature of the device 10 may remain upondiscontinuing the activation signal. In this embodiment, the device 10includes a means to maintain the change in active material 16, such as alatch, lock, stop and/or the like. Upon release of the means to maintainthe change in active material 16, the device 10 reverts back to theoriginal at least one feature. As previously discussed, the activationdevice 18, controller 24 and/or sensor 26 may function with each otherand the airflow control device 40 to initiate the changes in at leastone attribute of the active material 16.

In another embodiment as shown in FIGS. 5 and 6, an airflow controldevice 50 comprises an active material adapted to selectively change itsflexural modulus, which is utilized to regulate airflow through andabout the device. The device 50 comprises a flap 54 formed of an activematerial. For example, the flap 54 may comprise a shape memory polymer.In one embodiment, the memorized shape of the shape memory polymer wouldbe arranged so as to occlude or present a reasonable cross-section tothe incident airflow. Embedded within the shape memory polymer is somemeans to raise the temperature of the polymer. One of many possibleheating elements may be a high resistance flexible metal grid 52. Whenthe shape memory polymer flap 54 is in the stiff state (i.e. below theglass transition temperature for the shape memory polymer) it willelastically oppose the force of the incident flow, as long as the flowis below a critical flow rate. When switched to the soft state throughheating, the stiffness of the material will change, resulting in achange in the stiffness of the air diverting structure. This change instiffness may be tailored through geometrical means or by compositionalformulation. As a result, the ability of the structure to oppose theincident flow may be significantly and intentionally reduced such thatthe structure bends and flow is re-directed. This effect can also beused to increase the distance between the ground and the air deflector,thus reducing the risk of collision with low lying obstacles. Thiseffect will occur above a threshold flow rate. In the case of shapememory polymers with one-way shape memory, once the structure is in thesoft state it will not be able to return to the initial configurationunless the incident flow is reduced significantly. However, when theairflow is reduced, the shape memory polymer will return to the originalconfiguration. As an additional capability, the shape memory polymer canreduce or repair damage incurred through impacts with road debris orparking structures through the same mechanism that allows selectivediversion of airflow.

Other active material structures may also be used in this manner, suchas elastic structures that can be stiffened or weakened through theactivation of magnetorheological fluids or rubbers, orelectrorheological fluids. In these embodiments, the materials undergo adynamic change in stiffness upon activation, but generally do notexhibit a significant force upon return to their initial configuration.Example embodiments utilizing these materials include a parallel set ofsoft elastomer tubes filled with magnetorheological fluids might thatcan be used to form the body of the airflow control device.

For activation, magnetizing coils would be wrapped around each tube.When activated through the action of a current through the coils, theviscosity of the magnetorheological fluid increases dramatically.Magnetorheological rubber materials can be used in a similarconfiguration, although the changes in stiffness for these materials aresignificantly lower. In either embodiment, the structure becomes stiffand more able to oppose the incident airflow. Similarly, a pair offlexible conducting sheets (for instance, graphite impregnatedelastomer) separated by a layer of electrorheological fluids could actas a variable stiffness structure. When activated, theelectrorheological fluid becomes a gel that stiffly binds the twosheets, dramatically increasing the dynamic stiffness of the structure.

Optionally, a shape memory alloy may be used to provide selectivelyvariable stiffness modulation. In this embodiment, the airflow controldevice is stiff above the austenite finish temperature and soft andhighly deformable below the martensite finish temperature for the shapememory alloy to variably change the incident airflow path. The shapememory alloy may be in the form of a thin sheet, foil, mesh grid, or thelike. Hence, to oppose the flow, the shape memory alloy must be heated,and to allow flow past the diverter, the shape memory alloy must beallowed to cool. Depending on temperature, therefore, the shape memoryalloy will either resist or allow the incident airflow to flow past theairflow control device.

In another embodiment as shown in FIGS. 7 and 8, an airflow controldevice 60 comprises an active material 62 that functions as a hinge. Inthis case, a rigid air diverter flap 66 is operably connected to astationary surface of the vehicle. For the case of a SMP hinge (i.e.,62), activation of the hinge by increasing the temperature above thetransition temperature will allow the diverter flap 66 to rotate easilyin response to air flow, which can be used to change the direction of anincoming air stream. In contrast, by cooling the shape memory polymerbelow the transition temperature, the flap can be locked into thecurrent position, wherein the original position may be obtained byheating the polymer above the transition temperature without an incomingair stream. Similar functionality can be achieved using a shape memoryalloy hinge, wherein the martensite phase provides rotation due to itslower modulus whereas in the austenite phase, the hinge 62 becomes stiffand does not permit rotation. In contrast to the shape memory polymerhinge, heating the shape memory alloy hinge into austenite phase willforce a recovery into the trained shape and thus could also serve asactuation for the flap.

Methods of controlling vehicle airflow are disclosed. In one embodiment,the method first comprises positioning the airflow controlling device ofany one of or combination of the preceding embodiments, e.g., devices10, 20, 30, 40, 50, 60 so as to provide airflow in contact duringmovement of the vehicle, the airflow controlling device comprising abody and an active material in operative communication with the body,wherein the active material is operative to change at least oneattribute in response to an activation signal. Once positioned, anactivation signal is selectively introduced to the active material. Byselectively introducing the activation signal, the at least oneattribute of the active material changes.

In another embodiment, the method includes discontinuing the activationsignal to reverse the change of at least one attribute of the activematerial. In an additional embodiment, the method includes maintainingthe change in at least one attribute of the active material upondiscontinuation of the activation signal.

Other embodiments include optimizing the power requirements fortransitioning between well as occupying the various operational states.In general, the occupancy of the operation state is achieved throughactivation of the active material, which is maintained by applyingsufficient power to maintain the transformation of the material. Forexample, in the shape memory alloy material this implies that the shapememory alloy components must be maintained above their phasetransformation temperature. In the case of piezoelectric materials,sufficient voltage must be applied to maintain the desired deformation.This type of operation is referred to as power-on hold.

In order to obtain a power-off hold operation state (also referred to asa zero power hold operation state), whereby the activated state may bemaintained without additional power, numerous different approaches arepossible. These generally include using various external latchingmechanisms to support the activated state, as well as incorporating astiffness changing material, that may be “frozen” after deformation andused to maintain structural deformation.

The principal purpose of this latch is to allow for a zero power holdmechanism, but additional benefits are also accrued through the use ofthis latch. These additional benefits include a possibility to have thesurface break away from the latched configuration due to impact witheither a foreign object, or an increase in airflow volume above aprescribed rate.

Some possible approaches include a magnetic system, whereby a permanentmagnet can be engaged and disengaged to a ferromagnetic keeper by meansof temporarily magnetizing the keeper. This approach is advantageous inthat mechanical contact is not required and thus greater environmentalrobustness is expected. Another possible latch implementation is aspring-loaded pin and acceptor assembly. In this case, the pin willslide into the acceptor under the force stored in a spring in serieswith the pin. A electromagnetic solenoid actuator, or shape memory alloyspring could be used to disengage the pin, and therefore release thestructure. An additional latch scenario would be a combination ofmagnetic and active materials approaches whereby a permanent magnetattaches to a ferromagnetic keeper, and the keeper may be disengagedfrom the permanent magnet using an active materials based approach.Shape memory alloy wires or helical springs could be used to obtain thistype of functionality. This system is advantageous over the purelymagnetic approach in that the greater actuation energy density of activematerials as compared to electromagnetic actuation allows for compactlatch designs to be created, and miniaturization of this concept.

An exemplary zero power hold mechanism is illustrated in FIG. 9. Thelatch 80 comprises a permanent magnet 82 distally disposed on orintegrated into an arm 84 extending from a body 86 that is fixedlyattached to the airflow control device, e.g., device 60. During use, thepermanent magnet 82 can selective engage a ferromagnetic keeper 88 whenin contact or in close proximity to the keeper to provide a power-offhold mechanism.

An alternative approach that provides similar functionality, without theuse of additional external components is the incorporation of a shapememory polymer material into the architecture. This approach utilizesthe “shape fixity” aspect of shape memory polymers. In this embodiment,the polymer may be softened, deformed into a new shape using the activematerial based actuation previously described and hardened. At thispoint, if the active component is relaxed, the deformation of theelastic component may be maintained by support of the shape memorypolymer.

In addition to the use of shape memory polymers for power-off hold, itshould be noted that numerous other materials can be used in a similarcapacity. For instance, a bladder or tubule filled with a meltablecomponent such as wax, may accomplish the same goals. Operationally,such a structure and system would function as described above for shapememory polymers. Thermoplastics and thermosets are also known to reducetheir stiffness upon heating, and can “freeze” in place upon cooling.

The airflow control devices and methods of the present disclosure areable to selectively adjust features such as shape, dimension, stiffness,location, combinations thereof, and the like by changing the at leastone attribute of active material 16 to match the needs of differentdriving conditions. Changes in at least one attribute of active material16 include shape, dimension, stiffness, combinations thereof and thelike. Utilizing active materials 16 to affect these changes providedevices of increased simplicity and robustness, while reducing thenumber of failure modes, device volume and energy requirements foractivation due to higher energy densities.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about”. Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained bythe present disclosure. At the very least, and not as an attempt tolimit the application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should at least be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to a particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An air deflector 60 adapted for external use with a vehicle, and tomodify an airflow and thus a resulting driving condition of the vehicle,said deflector comprising: a hinge made from an active material 62fixedly connected to the vehicle and adapted to hingingly communicatewith a stationary surface, wherein the active material 62 is adapted tochange a flexural modulus property in response to an activation signal17; and a rigid flap 66 hingingly attached to the vehicle, via the hingemade from the active material.
 2. The air deflector 60 of claim 1,wherein the active material 62 comprises a shape memory alloy, a shapememory polymer, an electroactive polymer, magnetorheological elastomer,piezoelectric material or combinations comprising at least one of theforegoing materials.
 3. The air deflector 60 of claim 1, wherein theactive material 62 is a sheet, foil, or strip.
 4. The air deflector 60of claim 1, wherein the activation signal 17 comprises a thermalactivation signal, an electrical activation signal, magnetic signal or acombination comprising at least one of the foregoing signals.
 5. The airdeflector 60 of claim 1, further comprising an activation device 18adapted to provide an activation signal 17 to the air deflector
 60. 6.The air deflector 60 of claim 1, further comprising at least one sensor26 and a controller 24 in operative communication with the activematerial
 62. 7. The air deflector 60 of claim 1, wherein the activationsignal 17 is triggered by a predetermined speed of the vehicle 100,wherein the flexural modulus of the active material changes when a speedof the vehicle 100 exceeds the predetermined speed.